Luma intra mode signaling

ABSTRACT

A coding apparatus configured to select an intra prediction mode for a current block, encode the selected intra prediction mode using truncated binary coding every time the selected intra prediction mode is a remaining mode, and encode the selected intra prediction mode using N bits when the selected intra prediction mode is included in a first portion from remaining modes and using N+1 bits when the selected intra prediction mode is included in a second portion of the remaining modes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 17/518,254, filed Nov. 3, 2021, which is a continuation ofco-pending U.S. patent application Ser. No. 16/899,313, filed Jun. 11,2020, which is a continuation of International Application No.PCT/US2019/031347 filed on May 8, 2019, which claims the benefit of U.S.Provisional Patent Application No. 62/696,739, filed Jul. 11, 2018, eachof which is hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to luma intra mode signaling.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

A first aspect relates to a method of coding implemented by a codingapparatus. The method includes selecting, using the coding apparatus, anintra prediction mode for a current block; and encoding, using thecoding apparatus, the selected intra prediction mode using truncatedbinary coding when the selected intra prediction mode is a remainingmode. In an embodiment, the method includes determining that the intraprediction mode that was selected is within the remaining modes list.

As will be more fully explained below, the method improves the existingintra mode signaling scheme. Embodiments may be configured to code allremaining intra modes, e.g., all intra modes that are not in theMPM-list (a.k.a., “non-MPM modes”) and are signaled in the bitstream,using truncated binarization. By using truncated binarization for theremaining modes, codewords are used more efficiently.

In a first implementation form of the method according to the firstaspect as such, the method further comprises determining that theselected intra prediction mode falls outside a most probable modes (MPM)list.

In a second implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises encoding the selected intra prediction modeusing 5 bits when the selected intra prediction mode is one of a firstthree modes from remaining modes.

In a third implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises encoding the selected intra prediction modeusing N bits when the selected intra prediction mode is included in afirst portion from remaining modes and using N+1 bits when the selectedintra prediction mode is included in a second portion of the remainingmodes.

In a fourth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises encoding the intra prediction mode using 6bits when the selected intra prediction mode is not one of a first threemodes from remaining modes.

In a fifth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the remaining mode is one of 61 remaining modes.

In a sixth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the MPM list contains 6 modes and the remaining mode is one of 61remaining modes.

In a seventh implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,all modes either belong to the MPM list or to the remaining modes.

In an eighth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,all of the remaining modes are coded using the truncated binary coding.

In a ninth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises filling initial modes in a remaining modeslist using a predetermined default mode list.

In a tenth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the predetermined default mode list comprises a planar mode(PLANAR_IDX), a dc mode (DC_IDX), a vertical mode (VER_IDX), ahorizontal mode (HOR_IDX), an intra mode 2 (2), a vertical diagonal mode(VDIA_IDX), and a diagonal mode (DIA_IDX).

In an eleventh implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises filling initial modes in the remainingmodes list using an offset to angular modes included in the MPM list.

In a twelfth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the offset is +/−N, where N is an integer with a value of 1, 2, 3, or 4.

In a thirteenth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the offset is added only to a first of two of the angular modes in theMPM list.

In a fourteenth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises filling initial modes of a remaining modelist using modes of neighboring blocks not immediately adjacent to thecurrent block.

In a fifteenth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises filling initial modes of a remaining modeslist using modes of second tier neighbors of the current block insteadof first tier neighbors.

In a sixteenth implementation form of the method according to the firstaspect as such or any preceding implementation form of the first aspect,the method further comprises filling initial modes in the remainingmodes list based on a location of a majority of modes in the MPM listrelative to one of a planar mode (PLANAR_IDX), a dc mode (DC_IDX), avertical mode (VER_IDX), a horizontal mode (HOR_IDX), an intra mode 2(2), a vertical diagonal mode (VDIA_IDX), and a diagonal mode (DIA_IDX).

In a seventeenth implementation form of the method according to thefirst aspect as such or any preceding implementation form of the firstaspect, the method further comprises filling initial modes in theremaining modes list by: comparing each of the modes in the MPM list toa location of different modes within a default mode list; determiningthat a winning one of the different modes within the default mode listis nearest to a majority of the modes in the MPM list; and filling thefirst three modes in the remaining mode list with modes nearest to thewinning one of the different modes within the default mode list.

A second aspect relates to method of decoding implemented by a decodingapparatus. The method includes obtaining, by the decoding apparatus,truncated binary code; decoding, by the decoding apparatus, thetruncated binary code to obtain an intra prediction mode comprising aremaining mode; and generating, by the decoding apparatus, a currentblock using the intra prediction mode that was obtained.

As will be more fully explained below, the method improves the existingintra mode signaling scheme. Embodiments may be configured to decode thetruncated binary code to obtain an intra prediction mode, which is oneof the remaining modes encoded using truncated binary coding. By usingtruncated binarization for the remaining modes, codewords are used moreefficiently.

In a first implementation form of the method according to the secondaspect as such, the method further comprises determining that the intraprediction mode is outside a most probable modes (MPM) list.

In a second implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, the method further comprises decoding the intra prediction modeusing 5 bits when the intra prediction mode was one of a first threemodes from remaining modes.

In a third implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, the method further comprises decoding the intra prediction modeusing 6 bits when the intra prediction mode is outside a first threemodes from remaining modes.

In a fourth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, the remaining mode is one of 61 remaining modes.

In a fifth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, there are 6 modes in the MPM list and 61 modes in the remainingmodes.

In a sixth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, all intra-prediction modes either belong to the MPM list or tothe remaining modes.

In a seventh implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, all of the remaining modes are coded using the truncated binarycoding.

In an eighth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, initial modes in a remaining modes list are from a predetermineddefault mode list.

In a ninth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, the predetermined default mode list comprises a planar mode(PLANAR_IDX), a dc mode (DC_IDX), a vertical mode (VER_IDX), ahorizontal mode (HOR_IDX), an intra mode 2 (2), a vertical diagonal mode(VDIA_IDX), and a diagonal mode (DIA_IDX).

In a tenth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, initial modes in the remaining modes list are based on an offsetto angular modes included in the MPM list.

In an eleventh implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, the offset is +/−N, where N is an integer with a value of 1, 2,3, or 4.

In a twelfth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, the offset is added only to a first of two of the angular modesin the MPM list.

In a thirteenth implementation form of the method according to thesecond aspect as such or any preceding implementation form of the secondaspect, initial modes in the remaining modes list are based on modes ofneighboring blocks not immediately adjacent to the current block.

In a fourteenth implementation form of the method according to thesecond aspect as such or any preceding implementation form of the secondaspect, initial modes in the remaining modes list are based on modes ofsecond tier neighbors of the current block instead of first tierneighbors.

In a fifteenth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, initial modes in the remaining modes list are based on alocation of a majority of modes in the MPM list relative to one of aplanar mode (PLANAR_IDX), a dc mode (DC_IDX), a vertical mode (VER_IDX),a horizontal mode (HOR_IDX), an intra mode 2 (2), a vertical diagonalmode (VDIA_IDX), and a diagonal mode (DIA_IDX).

In a sixteenth implementation form of the method according to the secondaspect as such or any preceding implementation form of the secondaspect, initial modes in the remaining modes list were determined by:comparing each of the modes in the MPM list to a location of differentmodes within a default mode list; determining that a winning one of thedifferent modes within the default mode list is nearest to a majority ofthe modes in the MPM list; and filling the first three modes in theremaining mode list with modes nearest to the winning one of thedifferent modes within the default mode list.

In a seventeenth implementation form of the method according to thesecond aspect as such or any preceding implementation form of the secondaspect, the different modes within the mode category comprise a planarmode (PLANAR_IDX), a dc mode (DC_IDX), a vertical mode (VER_IDX), ahorizontal mode (HOR_IDX), an intra mode 2 (2), a vertical diagonal mode(VDIA_IDX), and a diagonal mode (DIA_IDX).

A third aspect relates to an encoding apparatus configured to performany of the preceding encoding methods.

A fourth aspect relates to a decoding apparatus configured to performany of the preceding decoding methods.

A fifth aspect relates to an encoding apparatus including a memory; anda processor coupled to the memory, the processor configured to: selectan intra prediction mode for a current block; encode the selected intraprediction mode using truncated binary coding when the selected intraprediction mode is a remaining node.

In a first implementation form of the encoding apparatus according tothe fifth aspect as such, the encoding apparatus comprises a transmittercoupled to the processor, the transmitter configured to transmit theencoded selected intra prediction mode toward a decoding apparatus.

In a second implementation form of the encoding apparatus according tothe fifth aspect as such or any preceding implementation form of thefifth aspect, the processor is configured to implement one or more ofthe preceding aspects or implementations.

Further implementation forms of the encoding apparatus correspond to therespective implementation forms of the encoding method according to thefirst aspect.

A sixth aspect relates to a decoding apparatus including a receiverconfigured to obtain a truncated binary code; a processor coupled to thereceiver, the processor configured to: decode the truncated binary codeto obtain an intra prediction mode comprising a remaining mode; andgenerate a current block using the intra prediction mode that wasobtained.

In a first implementation form of the decoding apparatus according tothe sixth aspect as such, the decoding apparatus comprises a displaycoupled to the processor, the display configured to display an imagegenerated using the current block.

In a second implementation form of the encoding apparatus according tothe sixth aspect as such or any preceding implementation form of thesixth aspect, the processor is configured to implement one or more ofthe preceding aspects or implementations.

Further implementation forms of the decoding apparatus correspond to therespective implementation forms of the decoding method according to thesecond aspect.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.Further details of embodiments are provided in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a block diagram illustrating an example coding system that mayutilize context modeling techniques.

FIG. 2 a block diagram illustrating an example video encoder that mayimplement context modeling techniques.

FIG. 3 a block diagram illustrating an example video decoder that mayimplement context modeling techniques.

FIG. 4 is a schematic diagram of a current coding unit and fiveneighboring blocks.

FIG. 5 is a schematic diagram of a current coding unit, first tierneighbors, and second tier neighbors.

FIG. 6 is a schematic diagram of an example of 67 intra predictionmodes.

FIG. 7 is a schematic diagram of an example video coding device.

DETAILED DESCRIPTION

It should be understood at the outset that the disclosed systems and/ormethods may be implemented using any number of techniques, whethercurrently known or in existence. The disclosure should in no way belimited to the illustrative implementations, drawings, and techniquesillustrated below, including the exemplary designs and implementationsillustrated and described herein.

FIG. 1 is a block diagram illustrating an example coding system 10 thatmay be suitable for implementing various video coding, prediction orcompression techniques. As shown in FIG. 1 , the coding system 10includes a source device 12 that provides encoded video data to bedecoded at a later time by a destination device 14. In particular, thesource device 12 may provide the video data to destination device 14 viaa computer-readable medium 16. Source device 12 and destination device14 may comprise any of a wide range of devices, including desktopcomputers, notebook (i.e., laptop) computers, tablet computers, set-topboxes, telephone handsets such as so-called “smart” phones, so-called“smart” pads, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, source device 12 and destination device 14 may be equippedfor wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, digital video disks (DVD)s, Compact DiscRead-Only Memories (CD-ROMs), flash memory, volatile or non-volatilememory, or any other suitable digital storage media for storing encodedvideo data. In a further example, the storage device may correspond to afile server or another intermediate storage device that may store theencoded video generated by source device 12. Destination device 14 mayaccess stored video data from the storage device via streaming ordownload. The file server may be any type of server capable of storingencoded video data and transmitting that encoded video data to thedestination device 14. Example file servers include a web server (e.g.,for a website), a file transfer protocol (FTP) server, network attachedstorage (NAS) devices, or a local disk drive. Destination device 14 mayaccess the encoded video data through any standard data connection,including an Internet connection. This may include a wireless channel(e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriberline (DSL), cable modem, etc.), or a combination of both that issuitable for accessing encoded video data stored on a file server. Thetransmission of encoded video data from the storage device may be astreaming transmission, a download transmission, or a combinationthereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, coding system 10 may be configured tosupport one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

In the example of FIG. 1 , source device 12 includes video source 18,video encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoder 30, and display device 32. Inaccordance with this disclosure, video encoder 20 of source device 12and/or the video decoder 30 of the destination device 14 may beconfigured to apply the techniques for bidirectional prediction. Inother examples, a source device and a destination device may includeother components or arrangements. For example, source device 12 mayreceive video data from an external video source, such as an externalcamera. Likewise, destination device 14 may interface with an externaldisplay device, rather than including an integrated display device.

The illustrated coding system 10 of FIG. 1 is merely one example.Techniques for bidirectional prediction may be performed by any digitalvideo encoding and/or decoding device. Although the techniques of thisdisclosure generally are performed by a video coding device, thetechniques may also be performed by a video encoder/decoder, typicallyreferred to as a “CODEC.” Moreover, the techniques of this disclosuremay also be performed by a video preprocessor. The video encoder and/orthe decoder may be a graphics processing unit (GPU) or a similar device.

Source device 12 and destination device 14 are merely examples of suchcoding devices in which source device 12 generates coded video data fortransmission to destination device 14. In some examples, source device12 and destination device 14 may operate in a substantially symmetricalmanner such that each of the source and destination devices 12, 14includes video encoding and decoding components. Hence, coding system 10may support one-way or two-way video transmission between video devices12, 14, e.g., for video streaming, video playback, video broadcasting,or video telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video.

In some cases, when video source 18 is a video camera, source device 12and destination device 14 may form so-called camera phones or videophones. As mentioned above, however, the techniques described in thisdisclosure may be applicable to video coding in general, and may beapplied to wireless and/or wired applications. In each case, thecaptured, pre-captured, or computer-generated video may be encoded byvideo encoder 20. The encoded video information may then be output byoutput interface 22 onto a computer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from source device 12 and produce a disc containing the encodedvideo data. Therefore, computer-readable medium 16 may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., group of pictures (GOPs). Display device 32 displays thedecoded video data to a user, and may comprise any of a variety ofdisplay devices such as a cathode ray tube (CRT), a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to the HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe International Telecommunications Union TelecommunicationStandardization Sector (ITU-T) H.264 standard, alternatively referred toas Moving Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding(AVC), H.265/HEVC, or extensions of such standards. The techniques ofthis disclosure, however, are not limited to any particular codingstandard. Other examples of video coding standards include MPEG-2 andITU-T H.263. Although not shown in FIG. 1 , in some aspects, videoencoder 20 and video decoder 30 may each be integrated with an audioencoder and decoder, and may include appropriatemultiplexer-demultiplexer (MUX-DEMUX) units, or other hardware andsoftware, to handle encoding of both audio and video in a common datastream or separate data streams. If applicable, MUX-DEMUX units mayconform to the ITU H.223 multiplexer protocol, or other protocols suchas the user datagram protocol (UDP).

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice. A device including video encoder 20 and/or video decoder 30 maycomprise an integrated circuit, a microprocessor, and/or a wirelesscommunication device, such as a cellular telephone.

FIG. 2 is a block diagram illustrating an example of video encoder 20that may implement bidirectional prediction techniques. Video encoder 20may perform intra- and inter-coding of video blocks within video slices.Intra-coding relies on spatial prediction to reduce or remove spatialredundancy in video within a given video frame or picture. Inter-codingrelies on temporal prediction to reduce or remove temporal redundancy invideo within adjacent frames or pictures of a video sequence. Intra-mode(I mode) may refer to any of several spatial based coding modes.Inter-modes, such as uni-directional prediction (P mode) orbi-prediction (B mode), may refer to any of several temporal-basedcoding modes.

As shown in FIG. 2 , video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 2 , videoencoder 20 includes mode select unit 40, reference frame memory 64,summer 50, transform processing unit 52, quantization unit 54, andentropy coding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, and partition unit 48. For video block reconstruction, video encoder20 also includes inverse quantization unit 58, inverse transform unit60, and summer 62. A deblocking filter (not shown in FIG. 2 ) may alsobe included to filter block boundaries to remove blockiness artifactsfrom reconstructed video. If desired, the deblocking filter wouldtypically filter the output of summer 62. Additional filters (in loop orpost loop) may also be used in addition to the deblocking filter. Suchfilters are not shown for brevity, but if desired, may filter the outputof summer 50 (as an in-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into largest coding units (LCUs), andpartition each of the LCUs into sub-coding units (sub-CUs) based onrate-distortion analysis (e.g., rate-distortion optimization). Modeselect unit 40 may further produce a quadtree data structure indicativeof partitioning of a LCU into sub-CUs. Leaf-node CUs of the quadtree mayinclude one or more prediction units (PUs) and one or more transformunits (TUs).

The present disclosure uses the term “block” to refer to any of a CU,PU, or TU, in the context of HEVC, or similar data structures in thecontext of other standards (e.g., macroblocks and sub-blocks thereof inH.264/AVC). A CU includes a coding node, PUs, and TUs associated withthe coding node. A size of the CU corresponds to a size of the codingnode and is square in shape. The size of the CU may range from 8×8pixels up to the size of the treeblock with a maximum of 64×64 pixels orgreater. Each CU may contain one or more PUs and one or more TUs. Syntaxdata associated with a CU may describe, for example, partitioning of theCU into one or more PUs. Partitioning modes may differ between whetherthe CU is skip or direct mode encoded, intra-prediction mode encoded, orinter-prediction mode encoded. PUs may be partitioned to be non-squarein shape. Syntax data associated with a CU may also describe, forexample, partitioning of the CU into one or more TUs according to aquadtree. A TU can be square or non-square (e.g., rectangular) in shape.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a reference frame.Mode select unit 40 also provides syntax elements, such as motionvectors, intra-mode indicators, partition information, and other suchsyntax information, to entropy coding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference frame memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference frame memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Intra-prediction unit 46 may intra-predict a current block, as analternative to the inter-prediction performed by motion estimation unit42 and motion compensation unit 44, as described above. In particular,intra-prediction unit 46 may determine an intra-prediction mode to useto encode a current block. In some examples, intra-prediction unit 46may encode a current block using various intra-prediction modes, e.g.,during separate encoding passes, and intra-prediction unit 46 (or modeselect unit 40, in some examples) may select an appropriateintra-prediction mode to use from the tested modes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

In addition, intra-prediction unit 46 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM). Mode selectunit 40 may determine whether an available DMM mode produces bettercoding results than an intra-prediction mode and the other DMM modes,e.g., using rate-distortion optimization (RDO). Data for a texture imagecorresponding to a depth map may be stored in reference frame memory 64.Motion estimation unit 42 and motion compensation unit 44 may also beconfigured to inter-predict depth blocks of a depth map.

After selecting an intra-prediction mode for a block (e.g., aconventional intra-prediction mode or one of the DMM modes),intra-prediction unit 46 may provide information indicative of theselected intra-prediction mode for the block to entropy coding unit 56.Entropy coding unit 56 may encode the information indicating theselected intra-prediction mode. Video encoder 20 may include in thetransmitted bitstream configuration data, which may include a pluralityof intra-prediction mode index tables and a plurality of modifiedintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks, andindications of a most probable intra-prediction mode, anintra-prediction mode index table, and a modified intra-prediction modeindex table to use for each of the contexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation.

Transform processing unit 52 applies a transform, such as a discretecosine transform (DCT) or a conceptually similar transform, to theresidual block, producing a video block comprising residual transformcoefficient values. Transform processing unit 52 may perform othertransforms which are conceptually similar to DCT. Wavelet transforms,integer transforms, sub-band transforms or other types of transformscould also be used.

Transform processing unit 52 applies the transform to the residualblock, producing a block of residual transform coefficients. Thetransform may convert the residual information from a pixel value domainto a transform domain, such as a frequency domain. Transform processingunit 52 may send the resulting transform coefficients to quantizationunit 54. Quantization unit 54 quantizes the transform coefficients tofurther reduce bit rate. The quantization process may reduce the bitdepth associated with some or all of the coefficients. The degree ofquantization may be modified by adjusting a quantization parameter. Insome examples, quantization unit 54 may then perform a scan of thematrix including the quantized transform coefficients. Alternatively,entropy encoding unit 56 may perform the scan.

Following quantization, entropy coding unit 56 entropy codes thequantized transform coefficients. For example, entropy coding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy coding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain, e.g., for later use as areference block. Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of theframes of reference frame memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in reference framememory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

FIG. 3 is a block diagram illustrating an example of video decoder 30that may implement bidirectional prediction techniques. In the exampleof FIG. 3 , video decoder 30 includes an entropy decoding unit 70,motion compensation unit 72, intra-prediction unit 74, inversequantization unit 76, inverse transformation unit 78, reference framememory 82, and summer 80. Video decoder 30 may, in some examples,perform a decoding pass generally reciprocal to the encoding passdescribed with respect to video encoder 20 (FIG. 2 ). Motioncompensation unit 72 may generate prediction data based on motionvectors received from entropy decoding unit 70, while intra-predictionunit 74 may generate prediction data based on intra-prediction modeindicators received from entropy decoding unit 70.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. Entropy decoding unit 70 forwardsthe motion vectors and other syntax elements to motion compensation unit72. Video decoder 30 may receive the syntax elements at the video slicelevel and/or the video block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (i.e., B, P, or GPB) slice,motion compensation unit 72 produces predictive blocks for a video blockof the current video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference frame memory 82.

Motion compensation unit 72 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Data for a texture image corresponding to a depth map may be stored inreference frame memory 82. Motion compensation unit 72 may also beconfigured to inter-predict depth blocks of a depth map.

Although certain embodiments are described herein using the concept ofslices, embodiments may use tiles and/or tile groups instead of oradditional to slices.

Definitions of Acronyms & Glossary

-   -   CTU/CTB—Coding Tree Unit/Coding Tree Block    -   CU/CB—Coding Unit/Coding Block    -   PU/PB—Prediction Unit/Prediction Block    -   TU/TB—Transform Unit/Transform Block    -   HEVC—High Efficiency Video Coding

Video coding schemes such as H.264/AVC and HEVC are designed along thesuccessful principle of block-based hybrid video coding. Using thisprinciple a picture is first partitioned into blocks and then each blockis predicted by using intra-picture or inter-picture prediction.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are studying thepotential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard (including its current extensions and near-termextensions for screen content coding and high-dynamic-range coding). Thegroups are working together on this exploration activity in a jointcollaboration effort known as the Joint Video Exploration Team (JVET) toevaluate compression technology designs proposed by their experts inthis area.

The VTM (Versatile Test Model) standard uses 35 Intra modes whereas theBMS (Benchmark Set) uses 67 Intra modes. To code the 67 intra modes, thecurrent intra mode coding scheme in BMS uses the following method.

To accommodate the increased number of directional Intra modes in BMS,an Intra mode coding method with 6 Most Probable Modes (MPMs) is used.Two major technical aspects are involved.

-   -   1) the derivation of 6 MPMs, and    -   2) entropy coding of 6 MPMs and non-MPM modes.

In BMS, the modes included into the MPM lists are classified into threegroups: Neighbor intra modes, Derived intra modes, and Default intramodes.

FIG. 4 depicts a current coding unit 400 and five neighboring blocks402. The current coding unit 400 may also be referred to as a currentcoding block. Five neighboring intra prediction modes, or in other wordsintra prediction modes of five neighboring blocks, are used to form theMPM list. Those locations of the 5 neighboring blocks are the same asthose used in the merge mode, i.e., left (L), above (A), below left(BL), above right (AR), and above left (AL) as shown in FIG. 4 . Aninitial MPM list is formed by inserting 5 neighbor intra modes, planar,and DC modes into the MPM list. A pruning process is used to remove theduplicated modes so that only unique modes are included into the MPMlist. The order in which the initial modes are included is left, above,planar, DC, below left, above right, and above left.

If the MPM list is not full (i.e. has less than 6 MPM candidates in thelist), derived modes are added, those intra modes are obtained by adding−1 or +1 to the angular modes which are already included in the MPMlist. Derivation is not applied to non-angular modes, i.e. DC or planar.

Finally, if the MPM list is still not complete, the default modes areadded in the order of: vertical, horizontal, intra mode 2, and diagonalmode. In FIG. 6 these modes are shown as HOR_IDX, DIA_IDX, MODE2 andVER_IDX, respectively. A s a result of this process, a unique list of 6MPM modes is generated.

For entropy coding of 6 MPMs, a truncated unary binarization of the MPMsis used. The first three bins are coded with contexts which depend onthe MPM mode related to the bin currently being signaled. The MPM modeis classified into one of three categories: (a) whether the mode belongsto horizontal (MPM mode is less than or equal to a diagonal direction),(b) vertical (MPM mode greater than the diagonal direction), or (c)non-angular (DC and planar) class. Accordingly, three contexts are usedto signal the MPM index.

The coding of the remaining 61 non-MPMs is done as follows. The 61non-MPMs are firstly divided into two sets: a selected modes set and anon-selected modes set. The selected modes set contains 16 modes and therest (45 modes) are assigned to the non-selected modes set. The mode setthat the current mode belongs to is indicated in the bitstream with aflag. Then, the mode from the selected set is signaled with a 4-bitfixed-length code, and the mode from the non-selected set is coded witha truncated binary code. The selected modes set is generated bysub-sampling the total 61 non-MPM modes with indexes as follows:

-   -   Selected modes set={0, 4, 8, 12, 16, 20 . . . 60}    -   Non-selected modes set={1, 2, 3, 5, 6, 7, 9, 10 . . . 59}

The summary of the different INTRA mode signaling mechanisms is shown inTable 1.

TABLE 1 Current LUMA Intra mode signaling in BMS Intra prediction modesMPM flag Selected flag Bin String MPM (6) 1 0 10 110 1110 11110 11111Selected modes (16) 0 1 4 bits fixed length code Non-selected modes 0 0Truncated binary code (45)

The present disclosure targets improvement in the intra mode signalingscheme.

Intra mode coding scheme currently described in BMS is consideredcomplex and therefore a cleaner solution is desired.

A disadvantage of the selected modes set is that the index list isalways constant and not adaptive based on the current block properties(for e.g. its neighboring blocks INTRA modes). A disadvantage ofnon-selected mode set is that the index list is always constant and notadaptive based on the current block properties (for e.g. its neighboringblocks INTRA modes).

In the present disclosure, an intra mode signaling scheme with 6 MPM andremaining 61 modes is proposed, wherein the remaining 61 modes are codedusing a truncated binarization scheme. The most probable modes may alsobe referred to as most probable intra prediction modes, and theremaining modes may also be referred to as remaining intra predictionmodes. Thus, embodiments may be configured to code all remaining intramodes, i.e. all intra modes that are not comprised in the MPM-list (inshort “non-MPM modes”) and are signaled in the bitstream, usingtruncated binarization. The remaining 61 intra modes can as well becoded using a fixed length code of 6 bits, but the disadvantage with thefixed length code of 6 bits is that out of the 64 possible codewords,only 61 codewords are used and 3 remaining code words are not used.Instead of a fixed length code, truncated binarization is proposed,which would use only 5 bits to signal the first 3 remaining modes andthe remaining 58 modes are then coded using 6 bits. The 6 MPM modes are,e.g., coded using unary coding. Further embodiments may be configured touse an MPM-list and a remaining modes list with a different number ofintra modes, e.g. an MPM list comprising more or less than 6 modes, anda remaining modes list comprising more or less than 61 modes.Embodiments may be in particular advantageous in case the number ofremaining modes does not equal a power of two because fixed lengthcoding would not use all possible code words efficiently. Embodimentsusing truncated binary coding may signal a few modes using less bitscompared to the other modes of the remaining modes and thus signal theremaining modes more efficient.

Embodiments of an encoding method may comprise selecting an intraprediction mode for a current block; and encoding the intra predictionmode using truncated binary coding when the selected intra predictionmode is a remaining mode. The remaining mode may be comprised in or bepart of a set or plurality of remaining modes, e.g. a remaining modelist. Embodiments may further comprise determining that the intraprediction mode is not comprised in (or is outside) an MPM list, andencoding the selected intra prediction mode using truncated binarycoding. In embodiments, the selected intra prediction mode is notcomprised in (or is outside of) an MPM list. Embodiments may comprise anMPM list and the remaining modes, e.g. only the MPM list and theremaining modes (non-MPM modes) and do not distinguish further sets ofintra-prediction modes for coding or signaling, wherein none of theintra prediction modes of the remaining modes is comprised in the MPMlist. In embodiments, the MPM list may comprise 6 intra prediction modesand the remaining modes may comprise 61 modes. Embodiments may compriseadding the truncated binary code to a bitstream. Further embodimentscomprise an encoder, e.g. an encoding apparatus or device, configured toperform any of the encoding methods.

Embodiments of a decoding method may comprise obtaining an truncatedbinary code, e.g. by parsing a bitstream or by other means; decoding thetruncated binary code to obtain an intra prediction mode of a remainingmode, e.g. from a plurality or set of remaining modes; and generating acurrent block using the intra prediction mode that was obtained. Thefurther features described with regard to the encoding method equally orcorrespondingly apply to the respective decoding embodiments. Furtherembodiments comprise a decoder, e.g. a decoding apparatus or device,configured to perform any of the decoding methods.

Several solutions are proposed to fill the first three modes of theremaining modes list.

The first three modes in the remaining modes list can be filled inseveral possible ways.

First, by using the modes from a predetermined default mode list whichis {planar mode (PLANAR_IDX, which corresponds to index “0”), dc mode(DC_IDX, which corresponds to index “1”), vertical mode (VER_IDX),horizontal mode (HOR_IDX), intra mode 2 (MODE2, which corresponds toindex “2”), vertical diagonal mode (VDIA_IDX), and diagonal mode(DIA_IDX)} (the terms in the brackets show the corresponding terms inFIG. 6 , further details about FIG. 6 are provided below, the defaultmode list only comprises intra-prediction modes and may also be referredto as default intra prediction mode list).

Second, by using offsets to the angular modes (angular intra-predictionmodes) which are already present in the MPM list. Here, the offset canbe +/−N, where N is a possible integer value whose value is {1, 2, 3,4}. The offsets could be added only to the first two angular modes fromthe MPM list.

Third, the intra modes (angular intra-prediction modes) of non-adjacentneighbors can also be used to fill the three modes. FIG. 5 depicts acurrent coding unit 500, first tier neighbors 502, and second tierneighbors 504. As shown in FIG. 5 , second tier neighbors intra modescan used.

Fourth, as shown in FIG. 6 , in a first step, a given mode from an MPMlist is taken and is checked if it is “nearby” to one of the followingmode categories {DC_IDX, HOR_IDX, DIA_IDX, VER_IDX, VDIA_IDX}, in asecond step, the mode categories are then “sorted” based on the“majority” of modes which are close to it. In a third step, theremaining modes list is generated by inserting modes which are nearby tothe winning mode category from step 2.

FIG. 6 shows an example of 67 intra prediction modes, e.g., as proposedfor VVC, the plurality of intra prediction modes of 67 intra predictionmodes comprising: planar mode (index 0), dc mode (index 1), and angularmodes with indices 2 to 66, wherein the left bottom angular mode in FIG.3 refers to index 2 and the numbering of the indices being incrementeduntil index 66 being the top right most angular mode of FIG. 6 .

The processing circuitry can be implemented in hardware, or in acombination of hardware and software, for example by a softwareprogrammable processor or the like.

FIG. 7 is a schematic diagram of a network device 700 according to anembodiment of the disclosure. The network device 700 is suitable forimplementing the disclosed embodiments as described herein. The networkdevice 700 comprises ingress ports 710 and receiver units (Rx) 720 forreceiving data; a processor, logic unit, or central processing unit(CPU) 730 to process the data; transmitter units (Tx) 740 and egressports 750 for transmitting the data; and a memory 760 for storing thedata. The network device 700 may also comprise optical-to-electrical(OE) components and electrical-to-optical (EO) components coupled to theingress ports 710, the receiver units 720, the transmitter units 740,and the egress ports 750 for egress or ingress of optical or electricalsignals.

The processor 730 is implemented by hardware and software. The processor730 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 730 is in communication with theingress ports 710, receiver units 720, transmitter units 740, egressports 750, and memory 760. The processor 730 comprises a coding module770. The coding module 770 implements the disclosed embodimentsdescribed above. For instance, the coding module 770 implements,processes, prepares, or provides the various networking functions. Theinclusion of the coding module 770 therefore provides a substantialimprovement to the functionality of the network device 700 and effects atransformation of the network device 700 to a different state.Alternatively, the coding module 770 is implemented as instructionsstored in the memory 760 and executed by the processor 730.

The memory 760 comprises one or more disks, tape drives, and solid-statedrives and may be used as an over-flow data storage device, to storeprograms when such programs are selected for execution, and to storeinstructions and data that are read during program execution. The memory760 may be volatile and/or non-volatile and may be read-only memory(ROM), random access memory (RAM), ternary content-addressable memory(TCAM), and/or static random-access memory (SRAM).

Additional details of this disclosure are presented in the followingembodiments.

Embodiment 1. An apparatus for determining an adopted intra predictionmode on the basis of a most probable modes (MPM) list and a remainingmodes list having a first portion and a second portion, wherein theadopted intra prediction mode is one of a plurality of intra predictionmodes comprising a plurality of angular intra prediction modes forpredicting sample values of a current picture block, wherein theapparatus comprises a processing circuitry configured to: generate thefirst portion of the remaining modes list by including one or moreangular intra prediction modes determined on the basis of the mostprobable modes list such that the one or more angular intra predictionmodes of the first portion of the remaining modes list are close to arespective angular intra prediction mode of the most probable modeslist; and determine the adopted intra prediction mode, in case theadopted intra prediction mode is part of the first portion of theremaining modes list, using less bits for encoding or decoding theadopted intra prediction mode than in case the adopted intra predictionmode is part of the second portion of the remaining modes list.

Embodiment 2. The apparatus of embodiment 1, wherein the processingcircuitry is configured to generate the first portion of the remainingmodes list by: ranking a plurality of angular intra prediction modecategories according to the number and/or the direction of angular intraprediction modes of the most probable modes list falling within eachangular intra prediction mode category; and generating a first portionof the remaining modes list by including one or more angular intraprediction modes from the highest ranked angular intra prediction modecategory in the remaining modes list.

Embodiment 3. The apparatus of embodiment 2, wherein the first portionof the remaining modes list obtained from a predetermined default modelist comprising five angular intra prediction mode categories, namely dcmode (DC_IDX), vertical mode (VER_IDX), horizontal mode (HOR_IDX), intramode 2 (2), vertical diagonal mode (VDIA_IDX) and diagonal mode DIA_IDX,wherein an angular intra prediction mode of the most probable modes listfalling within each angular intra prediction mode category, for example,corresponds to associating each of the angular intra prediction modes ofthe most probable modes list to the angular intra prediction modecategory being closest to the corresponding angular intra predictionmode of the most probable modes list.

Embodiment 4. The apparatus of embodiment 2 or 3, wherein the processingcircuitry is further configured to complete the first portion of theremaining modes list by repeating step (ii) with the second highestranked angular intra prediction mode category.

Embodiment 5. The apparatus of embodiment 2 to 3, wherein each intraprediction mode is identified by an intra prediction mode index andwherein the processing circuitry is configured to define the pluralityof angular intra prediction mode categories on the basis of therespective angular intra prediction modes associated with a horizontaldirection, a vertical direction and one or more diagonal directions.

Embodiment 6. The apparatus of any one of the preceding embodiments,wherein each intra prediction mode is identified by an intra predictionmode index and wherein the processing circuitry is configured togenerate the first portion of the remaining modes list by including oneor more angular intra prediction modes in the first portion of theremaining modes list, whose respective intra prediction mode index hasan offset of +1, −1, +2, −2, +3, −3, +4 or −4 with respect to an intraprediction mode index of an angular intra prediction mode of the mostprobable modes list.

Embodiment 7. The apparatus of embodiment 6, wherein each list elementof the most probable modes list is identified by a most probable modesindex and wherein the processing circuitry is configured to generate thefirst portion of the remaining modes list by including one or moreangular intra prediction modes in the first portion of the remainingmodes list, whose respective intra prediction mode index has an offsetof +1, −1, +2, −2, +3, −3, +4 or −4 with respect to an intra predictionmode index of an angular intra prediction mode of the most probablemodes list.

Embodiment 8. The apparatus of embodiment 7, wherein the processingcircuitry is configured to generate the first portion of the remainingmodes list by including one or more angular intra prediction modes inthe first portion of the remaining modes list on the basis of aprocessing loop starting with the offset of +1 with respect to an intraprediction mode index of an angular intra prediction mode of the mostprobable modes list, which is incremented during each round of theprocessing loop, or with the offset of −1 with respect to an intraprediction mode index of an angular intra prediction mode of the mostprobable modes list, which is decremented during each round of theprocessing loop.

Embodiment 9. The apparatus of embodiment 8, wherein the processingcircuitry is configured to repeat the processing loop for an angularintra prediction mode of the most probable modes list having a smallmost probable modes index more often than the processing loop for anangular intra prediction mode of the most probable modes list having alarge most probable modes index.

Embodiment 10. The apparatus of embodiment 8, wherein the processingcircuitry is configured to generate the first portion of the remainingmodes list by including one or more angular intra prediction modes inthe first portion of the remaining modes list, whose respective intraprediction mode index has an offset of +2, −2, +4, −4, +6, −6, +8 or −8with respect to an intra prediction mode index of an angular intraprediction mode of the most probable modes list.

Embodiment 11. The apparatus of any one of the preceding embodiments,wherein the processing circuitry is further configured to generate thesecond portion of the remaining modes list by including those intraprediction modes of the plurality of intra prediction modes in thesecond portion of the remaining modes list that are not part of the mostprobable modes list and the first portion of the remaining modes list.

Embodiment 12. The apparatus of any one of the preceding embodiments,wherein the processing circuitry is further configured to be implementedin hardware, or in a combination of hardware and software.

Embodiment 13. The apparatus of any one of the preceding embodiments,wherein the processing circuitry is further configured to predict samplevalues of the current picture block using the adopted intra predictionmode and to provide a predicted picture block.

Embodiment 14. The apparatus according to embodiment 13, wherein theapparatus is an encoding apparatus, and wherein the processing circuitryis further configured to: encode the current picture block on the basisof the predicted picture block and the adopted intra prediction mode.

Embodiment 15. The apparatus according to embodiment 14, wherein theprocessing circuitry is further configured to signal a truncated binarycode for an intra prediction mode of the current picture block if theintra prediction mode belongs to the remaining modes list.

Embodiment 16. The apparatus according to embodiment 15, wherein theapparatus is a decoding apparatus, and wherein the processing circuitryis further configured to decode the current picture block on the basisof the predicted picture block and the adopted intra prediction mode.

Embodiment 17. The apparatus according to embodiment 16, wherein theprocessing circuitry is further configured to parse a truncated binarycode to determine an intra prediction mode of the current picture blockif the intra prediction mode belongs to the remaining modes list.

Embodiment 18. A method for determining an adopted intra prediction modeon the basis of a most probable modes list and a remaining modes listhaving a first portion and a second portion, wherein the adopted intraprediction mode is one of a plurality of intra prediction modescomprising a plurality of angular intra prediction modes for predictingsample values of a current picture block, wherein the method comprises:generating the first portion of the remaining modes list by includingone or more angular intra prediction modes determined on the basis ofthe most probable modes list such that the one or more angular intraprediction modes of the first portion of the remaining modes list areclose to a respective angular intra prediction mode of the most probablemodes list; and determining the adopted intra prediction mode, in casethe adopted intra prediction mode is part of the first portion of theremaining modes list, using less bits, for encoding or decoding theadopted intra prediction mode, than in case the adopted intra predictionmode is part of the second portion of the remaining modes list.

Embodiment 19. A computer program product comprising program code forperforming the method of embodiment 14 when executed on a computer or aprocessor.

Embodiment 20. The apparatus according to any one of the embodiments 1to 13, wherein the processing circuitry is further configured todetermine the first portion of the remaining modes list from apredetermined default mode list comprising or consisting of a planarmode (PLANAR_IDX), a dc mode (DC_IDX), a vertical mode (VER_IDX), anhorizontal mode (HOR_IDX), an intra mode 2 (2), a vertical diagonal mode(VDIA_IDX), and a diagonal mode (DIA_IDX).

Embodiment 21. The apparatus according to any one of the embodiments 1to 13, wherein the processing circuitry is further configured todetermine the first portion of the remaining modes list by including theintra prediction modes of second tier neighbors of the current pictureblock.

Embodiment 22. At both encoder and decoder, the intra mode is signaledby using truncated binarization for the non-MPM intra modes.

Embodiment 23. Since truncated binarization is used for coding 61non-MPMs, the first three modes will require 5 bits to be signaled andtherefore the first three modes in non-MPMs list are generated based onthe intra modes which are already included in the MPM list.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

1. A bitstream comprising an encoded intra prediction mode for a block,wherein intra prediction modes either belong to an MPM list or toremaining modes, wherein 6 modes are in the MPM list and 61 modes are inthe remaining modes, and when the intra prediction mode is a remainingmode, the intra prediction mode is encoded using truncated binarycoding, wherein the intra prediction mode is encoded using 5 bits whenthe intra prediction mode is one of a first three modes from theremaining modes, and the intra prediction mode is encoded using 6 bitswhen the intra prediction mode is outside a first three modes from theremaining modes.
 2. The bitstream of claim 1, wherein initial modes in aremaining modes list are from a predetermined default mode list.
 3. Thebitstream of claim 2, wherein the predetermined default mode listcomprises a planar mode (PLANAR_IDX), a dc mode (DC_IDX), a verticalmode (VER_IDX), a horizontal mode (HOR_IDX), an intra mode 2 (2), avertical diagonal mode (VDIA_IDX), and a diagonal mode (DIA_IDX).
 4. Thebitstream of claim 3, wherein initial modes in the remaining modes listhave an offset to angular modes included in the MPM list.
 5. Thebitstream of claim 4, wherein the offset is +/−N, where N is an integerwith a value of 1, 2, 3, or
 4. 6. The bitstream of claim 4, wherein theoffset is added only to a first of two of the angular modes in the MPMlist.
 7. The bitstream of claim 1, wherein initial modes of theremaining mode list comprise modes of neighboring blocks not immediatelyadjacent to the current block.
 8. The bitstream of claim 1, whereininitial modes of the remaining modes list comprise modes of second tierneighbors of the current block instead of first tier neighbors.